This invention relates to impulse or drop-on demand ink jet printers employing an array of ink jets which are capable of printing a substantial field of droplets on demand.
U.S. Pat. No. 4,714,934 discloses an ink jet apparatus of the type shown in FIGS. 1 through 3. The apparatus includes a print head 10 having a reservoir 12 and an imaging head of 14. The print head 10 is juxtaposed to a target 16 which is advanced by means of a transport system, including rollers 18 and 20, in an incremental fashion. As shown in FIG. 1, print head 10 includes an orifice plate 22, including orifices 24. In FIG. 1, the orifices are shown further apart from each other than they are in practice for purposes of illustration.
The orifices 24 actually comprise a plurality of sets of orifices which are more fully described with reference to FIGS. 2 and 3. The sets of orifices 24 are vertically displaced as a result of the inclination of the print head 10 with respect to the scanning direction depicted by arrow 26. The orifices 24 are arranged in groups of three (3) and inclined on the orifice plate 22 so as to be substantially vertical when the print head 10 is inclined with respect to the scanning direction 26 as shown in FIG. 1. The hash marks 28 and the orifice plate actually show this angle of inclination. The angle of the orifices 24 in each group with respect to the vertical as shown in FIG. 2 is chosen such that when the orifice plate 22 is inclined as shown in FIG. 1, sets of orifices 24 will be vertical. As scanning in the direction depicted by the arrow 26 proceeds, there is no overlap of any droplets projected from the orifices so as to permit the apparatus as shown in FIGS. 1 through 3 to create a vertical bar when the droplets are ejected sequentially in the proper timed relationship. Of course, the droplets can also produce an alphanumeric character by ejecting appropriate droplets on demand.
By changing the angle of inclination of the hash marks 28, it is possible to change the angle of inclination of the print head 14. However, if the angle of inclination is increased beyond a certain limit, it becomes impossible to print a continuous bar since the orifices cannot be spaced sufficiently close together to provide full coverage of the field. In addition, the chambers associated with those orifices become starved for ink when operated at a sufficiently high frequency. Moreover, it has not been possible to increase the number of chambers since cross-talk and limited real estate do not allow transducers to be coupled to the chambers.
As also shown in U.S. Pat. No. 4,714,934, the individual ink jets include feet which are coupled to the ink jet chambers. These feet 46 are secured to a foot plate by a resilient rubber-like material, such as silicone. As a consequence, ink within the ink jet chambers is exposed to a variety of materials including the foot, the silicone and the materials from which the remainder of the ink jet including the chamber and the orifices are made. This in turn produces compatibility problems which effectively limit the type of ink which may be employed in an ink jet apparatus.